In the case that a User Equipment (UE) communicates with a Relaying Party (RP), there is a need of a method of transmitting an identifier and identifying the user based on the identifier.
However, the conventional system has security vulnerability in the procedure of transmitting an identifier and verifying the identifier for Single Sign-On. That is, the security vulnerability of the Single Sign-On may result in phishing attack and therefore there is a need of a method for supporting the Single Sign-On efficiently by improving the related procedure.